Using automotive steering shafts and flanges as an example, the current method of manufacture consists of separate flanges and shafts manufactured as a subassembly. There are several disadvantages in the presently produced form of apparatus. Initially, as they are made from two pieces, an accident or some other form of abnormal loading such as severe terrain could cause separation of the two pieces resulting in loss of steering capability of the vehicle. Additionally, the torque strength is dependent upon the integrity of the joint of the two pieces and this joint is normally serrated. An abnormal shock load applied radially could shear the serrations causing the two parts to separate. An excessive axial loading can cause the two parts to become loose or even to separate longitudinally.
In the presently known construction, female serrations in the flange can be produced by means of broaching which is a reliable and consistent metal removal process. The serrations on the shaft are produced by the rolling process and are difficult to control to the required limits of accuracy that are necessary in order to obtain a totally reliable fit between the two parts. Additionally, the joint in the vicinity of the serrations is susceptible to deterioration from road salt and other corrosive substances which are used in large quantities in various parts of North America and particularly in Canada.
The two piece construction complicates quality control, scheduling of production, material procurement and parts control and is time consuming and costly to manufacture.
The weakness of the known two piece construction can contribute to serious malfunction or complete failure of a steering system of a vehicle. For example, if the joint between the two parts becomes loose, then backlash in the steering wheel is created which causes a lack of response when the steering wheel is rotated. Should the joint fail entirely and the two pieces become separated then the operator of the vehicle has no steering capability whatsoever.